Means for controlling the speed of a cable

ABSTRACT

The speed of a cable being unwound and wound onto a cable drum disposed on a movable vehicle is controlled by developing a control signal from an error signal which is the difference of an actual value representing the drum speed and a reference value which contains two components, one proportional to the vehicle speed and another proportional to the position of a tensioning means associated with the cable drum.

SUMMARY OF THE INVENTION

This invention relates to an apparatus for controlling the speed atwhich a cable is unwound from and would onto a cable drum disposed on amovable vehicle in general and more particularly to an improvedapparatus of this nature permitting operation over larger ranges ofdistance and velocity.

Various vehicles which are electrically driven such as mobile cranes,loading machines in mines and the like have a cable connection to afeeding source and thus include a cable drum onto which cable must beunwound or rewound as the vehicle moves away from or towards the feedingsource. When vehicles of this nature are driven at great speed or whenthey accelerate or decelerate rapidly, great demands are placed on thecontrol system for the cable drum. This is particularly true when thevehicle must have a large range of operating capability. With largedistance capabilities great amounts of cables must be wound on the drum.The greater the amount of cable which is wound on the drum, the greaterthe moment of inertia.

Because of these problems, prior art control devices have not beencompletely satisfactory for controlling cable drum drives in vehicles ofthis nature. Thus, the need for an improved cable drum drive system foruse in electrically driven vehicles becomes evident.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for controlling the drive ofthe cable drum and thus controlling the speed at which the cable iswound and unwound reliably under the types of conditions noted above.

In accordance with the present invention this is accomplished bymeasuring the actual cable drum speed, the speed of the vehicle and theposition of a tensioning spring associated with the cable drum drive.The difference between the actual drum speed and the sum of the vehiclespeed and tensioning device position is used to develop an error signalwhich is the input to a proportional integral controller. The controllerdevelops a control output which is used to control means for driving aDC motor having its shaft coupled to the cable drum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic elevation view illustrating cable drum equipmentdisposed on a movable vehicle.

FIG. 2 is a block diagram of the control apparatus of the presentinvention for controlling the cable speed in the system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a cable drum system of the type which is controlledby the apparatus of the present invention. Shown is a vehicle 10 movableon wheels 11 which ride on a base 12. Mounted on the vehicle 10 is acable drum 13 supported for rotation on a shaft 14. The shaft is coupledto a drive unit, not shown on FIG. 1 but to be described below inconnection with FIG. 2. A cable 15 is wound onto the drum 13. The cableruns from the drum 14 over traversing wheels 16 and 17, respectively.The shaft of the traversing wheel 16 is mechanically coupled to a springassembly 18 attached to the vehicle. The spring assembly 18 applies abias force in an upward direction to the traversing wheel 16. Windingand unwinding of the cable 15 applies a force to the wheel which opposesthe spring force. The traversing wheel 17 is fixed to the vehicle 10.Regulation of the cable speed will result in a regulation of the heightof the traversing wheel 16 as will be obvious to those skilled in theart.

FIG. 2 is a block diagram illustrating the improved apparatus of thepresent invention for controlling the cable drive of FIG. 1. Asillustrated, the cable drum 13 has its shaft 14 coupled to motor 19which may be, for example, a separately excited DC motor. The motor isdriven from a motor driver 30 which may be a double converter. Controlof DC motors using converters is well known in the art. See, forexample, Thyristor Phase-Controlled Converters and Cyclo-converters byB. P. Pelly, [John Wiley & Sons, 1971], particularly page 13 et seq.Such control is also disclosed in Harwood's Control of Electric Motorsby Ralph A. Miller--master [John Wiley and Sons, 1970]. In theillustrated embodiment there is shown a power input 31 which will besingle or 3-phase AC power which in the converter of the motor driver isrectified in a controlled manner in accordance with the control input online 33, as more fully described in the above-mentioned references.

The control signal on line 33 designated δ_(n) is obtained from a motorcontroller 20. The motor controller 20 is a proportional integralcontroller obtaining an input error ε from a summing junction 25. Thesumming junction 25 obtains as a first, actual value, input a quantityn_(a) from a direction sensitive tachometer generator 22 coupled bymeans of a shaft 23 to motor 19. The desired value inputs with which theactual value input n_(a) is summed at the summing junction 25 includes aquantity n_(b) proportional to vehicle speed and obtained from a seconddirection sensitive tachometer generator drive system and a quantity Δn_(b) representing the position of the traversing wheel 16 obtained froma position transducer 24. Position transducer 24 may, for example, be apotentiometer coupled to the traversing wheel 16. The positiontransducer 24 is preferably adjusted so that the quantity Δ n_(b) is 0at a preset level of the traversing wheel shaft 16 which is anintermediate position between the uppermost level of that shaft and alower level which can be reached through compression of the springassembly 18. What this means is that the quantity Δ n_(b) provides acontrol input to the motor controller 20 which causes it to regulate thedrive of motor 19 and thus the cable drive to cause the traversing wheel16 to remain in an intermediate position. This in turn allows the springassembly 18 to place a suitable mechanical tension on the cable 15 whileat the same time being able to move in both directions to absorbtemporary deviations. Thus, the output of the summing junction 25, ε,will contain a contribution representing the difference between actualspeed n_(a) and desired speed n_(b) [a quantity proportional to vehiclespeed] and a contribution representing the deviation of the traversingwheel 16 from its desired position. As noted above, this input signal εis provided to the motor controller 20 which is a proportional integralcontroller. For example, it may comprise an integrating amplifier whichchanges its output in response to input changes in order to develop anoutput δ_(n) which will result in a motor speed at which the errorsignal ε is zero.

What is claimed is:
 1. Apparatus for controlling the speed of a cablewhen being unwound and wound on a cable drum which is disposed on amovable vehicle said cable drum having associated therewith drive meanscomprisinga. means for measuring the speed of the vehicle and providinga first output signal proportional thereto; b. means for measuring thespeed of rotation of the cable drum and providing a second output signalproportional thereto; and c. control and regulating means having asinputs said first and second signals and providing as an output a thirdsignal which is related to the difference therebetween, said outputcoupled to control the drive means for said cable drum.
 2. Apparatusaccording to claim 1 and further including a traversing wheel over whichsaid cable runs when going to and from said cable drum said traversingwheel having a shaft which is spring biased and disposed for motion withrespect to the vehicle.
 3. Apparatus according to claim 2 and furtherincluding means for measuring the deviation of said traversing wheelfrom a preset level providing as an output a fourth signal proportionalthereto, said fourth signal being coupled as an additional input to saidcontrol and regulating means.
 4. Apparatus according to claim 3 whereinsaid control and regulating means comprise a summing junction havingsaid first, second and fourth signals as inputs and differencing the sumof said first and fourth signals and said second signal to develop afifth signal.
 5. Apparatus according to claim 4 wherein said control andregulating means further include a proportional integral controllerhaving as its input said fifth signal and providing its output as saidthird signal.
 6. Apparatus according to claim 5 wherein said drive meanscomprises a converter controlled DC motor and wherein said third signalis the control input to the converter of said motor.
 7. Apparatus forcontrolling the speed of a cable when being unwound and wound onto acable drum which is arranged on a movable vehicle comprising:a. a DCmotor coupled to the cable drum; b. a converter providing drive inputsto said DC motor; c. a spring loaded traversing wheel over which thecable runs; d. means for measuring the vehicle speed and providing afirst output signal proportional thereto; e. means for measuring thespeed of rotation of the cable drum and providing a second output signalproportional thereto; f. means for measuring the deviation of saidspring loaded wheel from a predetermined position and providing a thirdoutput signal proportional thereto; g. means for finding the differencebetween the sum of said first and third signals and said second signalto develop a difference signal; and h. a proportional integralcontroller having said difference signal as an input and providing itsoutput as a control input to said converter.